Dissimilar arm asymmetric radial or star block copolymers for adhesives and sealants

ABSTRACT

Radial or star asymmetric block copolymer of the following formulae and improved adhesive and sealant compositions containing them 
     
         (I) (A--HD).sub.x --Y--(UD).sub.z or (II) (UD--A--HD).sub.x --Y or (III) 
    
      ((UD) y  --A--HD) x  --Y--(UD) z   
     wherein A is a vinyl aromatic hydrocarbon block having a molecular weight of from 4000 to 20,000, HD is a hydrogenated conjugated diene block having a molecular weight of from 10,000 to 100,000, Y is a multifunctional coupling agent, UD is an unhydrogenated conjugated diene block having a molecular weight of from 1000 to 80,000, x is an integer from 2 to 20, y is 0 or 1, z is an integer from 1 to 10, and x+z ranges from 3 to 30.

BACKGROUND OF THE INVENTION

This invention is directed to adhesive and sealant compositions whichcontain dissimilar arm asymmetric radial block copolymers. Moreparticularly, the invention is related to such compositions containingasymmetric block copolymers which have both hydrogenated andunhydrogenated sets of arms.

Block copolymers have been employed in adhesive compositions for manyyears, primarily because of their high cohesive strengths and theirability to crosslink without a chemical vulcanization step. Blockcopolymers such as those described in U.S. Pat. No. 3,239,478 are eitherlinear or radial or star styrene-butadiene or styrene-isoprene blockcopolymers. The high cohesive strength of these polymers is often adetrimental quality in certain applications. In the past, cohesivestrength was reduced by adding a styrene-isoprene diblock copolymer tothe primary block copolymer to lower the cohesive strength and give lesselasticity and better conformability. U.S. Pat. No. 4,391,949 suggestedanother approach whereby a star-shaped asymmetric block copolymer havingstyrene-diene and diene homopolymer arms was used.

These conventional block copolymers when used in adhesives tend todegrade in processing and/or over time because they are unsaturated inthe main rubber chain. These unsaturation sites are reactive sites whichare vulnerable to attack, such as by free radicals created by oxidation,ultraviolet light or mechanical action. As a result, the polymer chainmay be severed by chain scission, reducing the molecular weight andthose properties which are sensitive to molecular weight. Alternatively,the unsaturation sites may be subjected to grafting and crosslinkingreactions which raise the molecular weight and undesirably stiffen thepolymer making it unprocessable or ineffective as an adhesive.Hydrogenating the conventional unsaturated base polymers creates anonpolar polymer which, although more stable, is difficult to tackifywith resin additives and which is therefore inferior to conventionalpolymers in some applications, including pressure sensitive adhesives.

The present invention offers a solution to some of these problemswithout sacrificing the adhesive qualities of unsaturated blockcopolymers. It does so by providing a polymer which has both unsaturatedand saturated arms.

SUMMARY OF THE INVENTION

The present invention provides improved adhesive and sealantcompositions which comprise a radial or star asymmetric block copolymerof the formulae

    (I) (A--HD).sub.x --Y--(UD).sub.z or (II) (UD--A--HD).sub.x --Y or (III) ((UD).sub.y --A--HD).sub.x --Y--(UD).sub.z

wherein A is a vinyl aromatic hydrocarbon block having a molecularweight of from 4000 to 20,000, HD is a hydrogenated conjugated dieneblock having a molecular weight of from 10,000 to 100,000, Y is amultifunctional coupling agent, UD is an unhydrogenated conjugated dieneblock having a molecular weight of from 1000 to 80,000, x is an integerfrom 2 to 20, preferably 2 to 4, y is 0 or 1, z is an integer from 1 to10, preferably 1 to 4, and x+z ranges from 3 to 30, preferably 3 to 6;and from 20 to 400 parts per 100 parts of copolymer of a tackifyingresin. These compositions may also contain resins which extend the dienephase, resins which reinforce and/or extend the vinyl aromatic phase,polyolefins, fillers, wax, stabilizers and reactive components designedto crosslink the polymers and/or resins.

DETAILED DESCRIPTION OF THE INVENTION

The primary novel component of the adhesive and sealant compositions ofthe present invention is the above-described block copolymer which hasboth saturated and unsaturated arms. The styrene-hydrogenated diene armsprovide the primary load bearing capability of the adhesive and sealantcompositions. It is important that these arms be hydrogenated so thatthe structural integrity of the polymer is preserved even if outsideforces cause degradation of the unsaturated side chains. The unsaturateddiene homopolymer arms are important in the composition to give thecomposition sufficient tack properties and/or the ability to betackified to make effective compositions, such as pressure sensitiveadhesive compositions.

The A blocks are polymer blocks of a vinyl aromatic hydrocarbon.Preferably, the vinyl aromatic hydrocarbon is styrene. Other usefulvinyl aromatic hydrocarbons include alphamethyl styrene, variousalkyl-substituted styrenes, alkoxy-substituted styrenes, vinylnaphthalene, vinyl toluene and the like. The HD and UD blocks arepolymer blocks of conjugated dienes. The preferred diene for the HDblocks is butadiene. Isoprene is preferred for the UD blocks. Otherdienes may also be used, including piperylene, methylpentadiene,phenylbutadiene, 3,4-dimethyl-1,3-hexadiene, 4,5-diethyl-1,3-octadieneand the like, preferably those conjugated dienes containing 4 to 8carbon atoms. It is preferred that the conjugated diene employed in theHD block differ from that employed in the UD block, especially inrespect to ease of hydrogenation.

The diene in the HD block should preferably hydrogenate faster and morecompletely than the diene in the UD block. The amount of hydrogenationin the unsaturated (UD) blocks after the reaction should be such that atleast 50 percent, preferably at least 75 percent, most preferably atleast 90 percent, of the original unsaturated diene remain unreacted.

The A--HD arms or blocks may be hydrogenated as generally described inthe prior art, preferably so as to reduce at least about 90 percent ofany olefinic double bonds in the polymer chains. Suitably at least 50percent, preferably at least 70 percent, and more preferably at least 90percent, most preferably at least 95 percent of the original olefinicunsaturation is hydrogenated.

The dienes used in this invention preferably should be those which arelargely amorphous at use temperatures (usually 10° C. to 40° C.) and donot contain excess crystallinity which would interfere with flexibility.For butadiene, e.g., the percent of 1,2 addition should preferably be 30percent to 65 percent to prevent excessive crystallinity afterhydrogenation to ethylene-butylene (EB) rubber. Below 30 percentcrystallinity is too high, giving a stiff polymer which is unsuitablefor pressure sensitive adhesives. Above 65 percent the Tg (glasstransition temperature) of the polymer is too high, making it difficultto formulate an acceptable pressure sensitive adhesive.

The preferred method for making the block copolymers of the presentinvention is basically described in European Patent Application0,314,256. Therein is disclosed a two-step process for producingasymmetric radial polymers which avoids the problem of the production ofthe unwanted homopolydiene polymer. The process involves separatelypolymerizing the monomers to create separately the two different typesof arms. Then one of the polymeric arms is coupled to the coupling agentand when that coupling reaction is complete, the second set of polymerarms is coupled to the coupling agent. This ensures that there will bevery little homopolydiene in the final polymer. In the presentinvention, for example, isoprene arms would be anionically polymerized,and coupled via the coupling agent. Subsequently or in parallel,styrene-butadiene (SB) arms would be anionically polymerized and atleast 2 arms then coupled to the isoprene arms via the coupling agent.These unhydrogenated precursors are useful as adhesives and sealants ontheir own but they suffer the stability problems common to polymers witha high degree of unsaturation (for example, (SB)₂ --Y--I₂).Subsequently, the coupled polymer is hydrogenated under conditions thatpreferably hydrogenate the diene of the A--HD arm (or block) only,leaving the diene of the UD arm (or block) essentially unsaturated.

In general, the method described is used to prepare asymmetric radial orstar polymers with any polymer containing a reactive end group whichwill react with one or more functional groups contained in the selectedcoupling agent. The method is particularly suitable for the preparationof asymmetric radial polymers from so-called "living" polymerscontaining a single terminal metal ion. As is well known in the priorart, "living" polymers are polymers containing at least one active groupsuch as a metal atom bonded directly to a carbon atom. "Living" polymersare readily prepared via anionic polymerization. Since the presentinvention is particularly well suited to the preparation of asymmetricradial polymers using "living" polymers to form the arms thereof, theinvention will be described by reference to such polymers. It will,however, be appreciated that the invention would be equally useful withpolymers having different reactive groups so long as the selectedcoupling agent contains functional groups which are reactive with thereactive site contained in the polymer.

Living polymers containing a single terminal group are, of course, wellknown in the prior art. Methods for preparing such polymers are taught,for example, in U.S. Pat. Nos. 3,150,209; 3,496,154; 3,498,960;4,145,298 and 4,238,202. Methods for preparing block copolymers such asthose preferred for use in the method of the present invention are alsotaught, for example, in U.S. Pat. Nos. 3,231,635; 3,265,765 and3,322,856. These patents are herein incorporated by reference. When thepolymer product is a random or tapered copolymer, the monomers are,generally, added at the same time, although the faster reacting monomermay be added slowly in some cases, while, when the product is a blockcopolymer, the monomer used to form the separate blocks are addedsequentially.

In general, the polymers useful as arms in the asymmetric radialpolymers of this invention may be prepared by contacting the monomer ormonomers with an organoalkali metal compound in a suitable solvent at atemperature within the range from -150° C. to 300° C., preferably at atemperature within the range from 0° C. to 100° C. Particularlyeffective polymerization initiators are organolithium compounds havingthe general formula:

    RLi

wherein R is an aliphatic, cycloaliphatic, alkyl-substitutedcycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbonradical having from 1 to 20 carbon atoms.

In general, the living polymers used as arms in the asymmetric radialpolymer will be contacted with the coupling agent at a temperaturewithin the range from 0° C. to 100° C. at a pressure within the rangefrom 0 bar to 7 bar and the contacting will be maintained until reactionbetween the arms and the coupling agent is complete or at leastsubstantially completed, generally for a period of time within the rangefrom 1 to 180 minutes.

In general, the polymers useful as arms in the asymmetric radialpolymers of this invention will be in solution when contacted with thecoupling agent. Suitable solvents include those useful in the solutionpolymerization of the polymer and include aliphatic, cycloaliphatic,alkyl-substituted cycloaliphatic, aromatic and alkyl-substitutedaromatic hydrocarbons, ethers and mixtures thereof. Suitable solvents,then, include aliphatic hydrocarbons such as butane, pentane, hexane,heptane and the like, cycloaliphatic hydrocarbons such as cyclohexane,cycloheptane and the like, alkyl-substituted cycloaliphatic hydrocarbonssuch as methylcyclohexane, methylcycloheptane and the like, aromatichydrocarbons such as benzene and the alkyl-substituted aromatichydrocarbons such as toluene, xylene and the like and ethers such astetrahydrofuran, diethylether, di-n-butyl ether and the like. Since thepolymers useful in making the asymmetric radial polymers of thisinvention will contain a single terminal reactive group, the polymersused in preparation of the asymmetric radial polymers will be retainedin solution after preparation without deactivating the reactive (living)site. In general, the coupling agents may be added to a solution of thepolymer or a solution of the polymer may be added to the coupling agent.

Any of the coupling agents known in the prior art to be useful informing a radial polymer by contacting the same with a living polymermay be used in both the method of this invention and the asymmetricradial polymers of this invention. Suitable coupling agents will containthree or more functional groups which will react with the living polymerat the metal-carbon bond. While the method of the present invention willimprove the relative distribution of different arms in an asymmetricradial polymer having any number of arms, the method is very effectivewhen the coupling agent contains from three to about twenty functionalgroups reactive with the metal-carbon bond of the "living" polymer.Suitable coupling agents, then include SIX₄, RSiX₃, HSiX₃, X₃ Si--SiX₃,RX₂ Si--(CH₂)_(x) --SiX₂ R, RX₂ Si(CH₂)_(x) --SiX₂ --(CH₂)_(x) --SiX₂ R,X₃ Si--(CH₂)_(x) --SiX₃, R--C(SiX₃)₃, R--C(CH₂ SiX₃)₃, C(CH₂ SiX₃)₄ andthe like, particularly those containing from three to about sixfunctional groups. In the foregoing formulae: each X may, independently,be fluorine, chlorine, bromine, iodine, alkoxide radicals, carboxylateradicals, hydride and the like; R is a hydrocarbyl radical having from 1to about 10 carbon atoms, preferably from 1 to about 6 carbon atoms; andx is a whole number from 1 to about 6. Particularly useful couplingagents include the silicon tetrahalides such as silicon tetrafluoride,silicon tetrachloride, silicon tetrabromide and the like, andbis(trihalo)silanes such as bis(trihalo)silylethane and hexahalodisilanewhere the halogen may be fluorine, chlorine, bromine, or iodine.

The coupling process per se is described in detail in U.S. Pat. No.4,096,203 which is herein incorporated by reference. Specificmultifunctional coupling agents useful herein are described in thatpatent but there are other coupling agents which may also be usefulherein.

Star polymers are made by coupling polymer arms using a polyfunctionalcoupling agent or coupling monomer. A preferred coupling agent is apolyalkenyl aromatic coupling agent such as those described in U.S. Pat.Nos. 4,010,226, 4,391,949 and 4,444,953, which are herein incorporatedby reference. U.S. Pat. No. 5,104,921, which is also herein incorporatedby reference, contains a complete description of such polyalkenylaromatic compounds at columns 12 and 13. Divinyl aromatic hydrocarbonscontaining up to 26 carbon atoms per molecule are preferred andparticularly divinyl benzene in either its meta, or para isomer andcommercial divinyl benzene which is a mixture of said isomers is alsoquite satisfactory. The coupling agent is preferably added to the livingpolymer after the polymerization is substantially complete. The amountof coupling agent varies between wide limits but preferably at least oneequivalent is used per equivalent of unsaturated living polymer to becoupled. The coupling reaction is generally carried out in the samesolvent as for the polymerization reaction. The temperature variesbetween wide limits, for example, from 25° C. to 95° C.

The hydrogenation of these copolymer arms may be carded out by a varietyof well established processes including hydrogenation in the presence ofsuch catalysts as Raney Nickel, noble metals such as platinum, palladiumand the like and soluble transition metal catalysts. Suitablehydrogenation processes which can be used are ones wherein thediene-containing polymer or copolymer is dissolved in an inerthydrocarbon diluent such as cyclohexane and hydrogenated by reactionwith hydrogen in the present of a soluble hydrogenation catalysts. Suchprocesses are disclosed in U.S. Pat. Nos. 3,113,986, 4,226,952 and Re.27,145, the disclosures of which are herein incorporated by reference.The polymers are hydrogenated in such a manner as to producehydrogenated polymers having a residual unsaturation content in thepolydiene block of less than about 20 percent, and preferably as closeto 0 percent as possible, of their original unsaturation content priorto hydrogenation. A titanium catalyst such as disclosed in U.S. Pat. No.5,039,755, which is herein incorporated by reference, may also be usedin the hydrogenation process.

In a preferred aspect of the invention, the asymmetric/dissimilar armstructure affords the possibility of augmenting the tack of saturatedpolymers by incorporation of freely rotating rubber chain ends in themolecule, which are more readily tackified by resin additives thanchains which are terminated by hard (polystyrene) blocks. An examplewould be a 6 arm polymer, 4 arms of which are polyisoprene and 2 ofwhich are poly(styrene-ethylene/butylene). Thepoly(styrene-ethylene/butylene) is hydrogenated poly(styrene-butadiene).This polymer is an example of a preferred radial polymer within thescope of formula (I) described above wherein A is styrene, HD isethylene/butylene (EB), x is 2, z is 4, Y is a hexafunctional couplingagent, and UD is polyisoprene. The freely rotating homopolymer chainends are readily tackified, while the copolymer arms provideload-bearing.

An especially preferred embodiment of the invention is (I--S--EB)_(x)--Y, where I is a polyisoprene block, S is a polystyrene block, EB is apoly(ethylene/butylene) rubber block, and x and Y have the meaningsdescribed previously. In this embodiment, hydrogenation of thepolybutadiene block to form the poly(ethylene/butylene) block is carriedout under conditions that are selective for polybutadiene reaction andessentially exclude hydrogenation of the polyisoprene block. Theunsaturated polyisoprene block is especially effective for impartingtack and peel strength to adhesive compositions.

The present invention also contemplates asymmetric/dissimilar armstructure radial and star polymers of the type described herein whichare entirely saturated. These polymers afford the possibility ofaugmenting the tack of saturated polymers by incorporation of freelyrotating rubber chain ends, albeit saturated chain ends, in the moleculewhich are more readily tackified by resin additives than chains whichare terminated by hard (polystyrene) blocks. An example would be a 4 armpolymer, 2 arms of which are hydrogenated polyisoprene and 2 arms ofwhich are hydrogenated poly(styrene-butadiene). The freely rotatingsaturated homopolymer chain ends are more readily tackified while thesaturated copolymer arms provide load-bearing.

The polymers of the present invention generally will have an A blockcontent (polystyrene content if A is styrene) of from 4 to 35 percent,preferably from 12 to 25 percent. This range provides the formulationlatitude to achieve acceptable tack and shear properties demanded by theparticular application. The polymers of the present invention preferablyhave a molecular weight of from 35,000 to 300,000. The A blocks have amolecular weight of from 4000 to 20,000. A blocks less than 4000 do notform domains of pure A and thus are not load-bearing. A blocks greaterthan 20,000 impart excess stiffness, thereby preventing pressuresensitivity in adhesives. The HD blocks should have a molecular weightof from 10,000 to 100,000. HD blocks less than 10,000 provide a weakpolymer with poor cohesive strength and low shear properties. HD blocksgreater than 100,000 make the rubber and adhesive compositions difficultto process. The UD blocks should have a molecular weight of from 1000 to80,000. UD blocks less than 1000 do not express tack and peel strengthimprovement in adhesives because they are not long enough to interactwith substrate surfaces. UD blocks greater than 80,000 soften theadhesive composition excessively, reducing cohesive strength and holdingpower.

Molecular weights are conveniently measured by Gel PermeationChromatography (GPC), where the GPC system has been appropriatelycalibrated. Polymers of known molecular weight are used to calibrate andthese must be of the same molecular structure and chemical compositionas the unknown block polymers that are measured. Anionically polymerizedlinear block polymers are close to monodisperse and it is bothconvenient and adequately descriptive to report the "peak" molecularweight of the narrow molecular weight distribution observed. The "peak"molecular weight is very nearly the same as the weight average molecularweight of the block polymer. For block polymers that are morepolydisperse, a weight average molecular weight should be measured bylight scattering or calculated from GPC data. Measurement of the truemolecular weight of the final coupled radial or star polymer is not asstraightforward or as easy to make using GPC. This is because the radialor star shaped molecules do not separate and elute through the packedGPC columns in the same manner as do the linear polymers used for thecalibration, and, hence, the time of arrival at a UV or refractive indexdetector is not a good indicator of the molecular weight. A good methodto use for a radial or star polymer is to measure the weight averagemolecular weight by light scattering techniques. The sample is dissolvedin a suitable solvent at a concentration less than 1.0 gram of sampleper 100 milliliters of solvent and filtered using a syringe and porousmembrane filters of less than 0.5 microns pore size directly into thelight scattering cell. The light scattering measurements are performedas a function of scattering angle and of polymer concentration usingstandard procedures. The differential refractive index (DRI) of thesample is measured at the same wavelength and in the same solvent usedfor the light scattering. The following references are hereinincorporated by reference:

1. Modem Size-Exclusion Liquid Chromatography, W. W. Yau, J. J.Kirkland, D. D. Bly, John Wiley & Sons, New York, N.Y., 1979.

2. Light Scattering from Polymer Solution, M. B. Huglin, ed., AcademicPress, New York, N.Y., 1972.

3. W. Kaye and A. J. Havlik, Applied Optics, 12, 541 (1973).

4. M. L. McConnell, American Laboratory, 63, May, 1978.

The saturated and/or unsaturated arms of the copolymers of the presentinvention may be functionalized, such as with polar groups whichincrease adhesion to many types of surfaces, especially high energysurfaces. For example, the unsaturated arms may be epoxidized orcarboxylated. Saturated arms may, for example, be maleated or silanated.Depending upon the type of functional group added, crosslinking may beaccomplished through these groups. Specific groups for this purposeinclude acids, such as carboxylic acids, anhydrides, such as carboxylicacid anhydrides, epoxidizing agents, acrylates, vinylalkoxysilanes andthe like.

The polymers, functionalized or unfunctionalized, of this invention maybe cured by ultraviolet or electron beam radiation, but radiation curingutilizing a wide variety of electromagnetic wavelength is feasible.Either ionizing radiation such as alpha, beta, gamma, X-rays and highenergy electrons or non-ionizing radiation such as ultraviolet, visible,infrared, microwave and radio frequency may be used.

The most common source of alpha, beta and gamma radiation areradioactive nuclei. An ionizing radiation source with commercial polymercrosslinking application is gamma radiation that is produced from eithercobalt-60 or cesium-137 radioactive nuclei. X-rays can be producedthrough deacceleration of high speed electrons through the electricfield of an atomic nucleus.

High voltage electron accelerators are preferred over gamma radiationand certain types of X-ray processing equipment. High energy electronsproduced by machine acceleration, as opposed to radioisotopes, can beapplied easily to industrial processes for the following reasons: easyon-off switching capability; less shielding is required than with gammaradiation; accelerator beams are directional and less penetrating thangamma or X-rays; and electron radiation provides high dose rates, i.e.maximum penetration per unit density of material, and is well suited foron-line, high speed processing applications. Commercially available highor low energy electron-processing equipment are the Dynamitron® device,dynacote, insulating-core transformer, linear accelerator, Van de Graaffaccelerator, pelletron, laddertron and linear cathode. Manufacturers ofhigh voltage electron-accelerator equipment are High Voltage EngineeringCorporation, Burlington, Mass. and Radiation Dynamics, Inc., Westbury,N.Y. Manufacturers of low energy electron beam generating equipmentinclude American International Technologies, Inc., of Torrance, Calif.;RPC Industries of Hayward, Calif.; and Energy Sciences of Wilmington,Mass.

Ultraviolet light sources may be based on the mercury-vapor arc. Mercuryis enclosed in a quartz tube and a potential is applied to electrodes ateither end of the tube. The electrodes can be of mercury, iron, tungstenor other metals. The pressure in the mercury-vapor lamp may be less than1 atm to more than 10 atm. As the mercury pressure and lamp operatingtemperatures are increased, the radiation becomes more intense and thewidth of the emission lines increases. Other UV light sources includeelectrodeless lamps, Xenon lamps, pulsed Xenon lamps, Argon ion lasersand Excimer lasers.

Visible light sources can be obtained from high pressure mercury arcs byaddition of rare gases or metal halides, which increase the number ofemission lines in the 350-600 nm region of the spectrum. Fluorescentlamps, tungsten halide lamps and visible lasers may also be utilized.

The presence of water in the polymer composition during the radiationcrosslinking is very undesirable due to the tendency of water toterminate the crosslinking. The radiation curing is therefore generallymore effective if the polymeric composition is at a temperature near orabove the boiling point of water at the time of the radiation curing.

The amount of radiation necessary for high gel formation varies with thethickness of the polymeric mass being irradiated, the amount ofunsaturation or, functionality, the extent to which the unsaturation orfunctionality is concentrated in specific regions within the polymericmass and the type of radiation utilized. When electron beam radiation isutilized, radiation doses of about 0.1 Mrads to about 16 Mrads areacceptable and from about 0.1 Mrads to about 5 Mrads are preferredbecause of equipment cost and possible damage to substrate material.

When using non-ionizing radiation it is necessary to employ aphotoinitiator to initiate the crosslinking reaction. Usefulphotoinitiators include diaryliodonium, alkoxy-substituteddiaryliodonium, triarylsulfonium, dialkylphenacylsulfonium, anddialkyl-4-hydroxyphenylsulfonium salts. The anions in these saltsgenerally possess low nucleophilic character and include SbF₆ --, BF₄--, PF₆ -- and AsF₆ --. Specific examples include(4-octyloxyphenyl)-phenyl-iodonium hexafluoroantimonate, UVI-6990 (fromUnion Carbide), and FX-512 (3M Company). Bis(dodecylphenyl)iodoniumhexafluoroantimonate, UV 9310C (GE), and, UVI-6974 (Union Carbide), areespecially effective. The onium salts can be used alone or inconjunction with a photosensitizer to respond to long wave length UV andvisible light. Examples of photosensitizers include thioxanthone,anthracene, perylene, phenothiazione, 1,2-benzathracene coronene, pyreneand tetracene. The photoinitiator and photosensitizer are chosen to becompatible with the polymer being crosslinked and the light sourceavailable.

Radiation induced cationic curing may also be done in combination withfree radical curing. Free radical curing can be further enhanced by theaddition of additional free radical photoinitiators and photosensitizersfor them.

Reactive (radiation curable) diluents that can be added to the polymerinclude alcohols, vinyl ethers, epoxides, acrylate and methacrylatemonomers, oligomers and polymers. They may also be blended with otherdiene-based polymers. Examples include bis(2,3-epoxy cyclopentyl)ethervinyl cyclohexene dioxide, limonene dioxide, epoxidized soya and linseedoils and fatty acids, vernonia oil, and UVI 6110 (Union Carbide).

The polymers may also be cured without the use of radiation by additionof a cationic initiator. Suitable initiators include the halides of tin,aluminum, zinc, boron, silicon, iron, titanium, magnesium and antimony,and the fluoroborates of many of these metals. BF₃ complexes such as BF₃-ether and BF₃ -amine are included. Also useful are strong Bronstedacids such as trifluoromethanesulfonic acid (triflic acid) and the saltsof triflic acid such as FC-520 (3M Company). The cationic initiator ischosen to be compatible with the polymer being crosslinked, the methodof application and cure temperature. The polymers may also becrosslinked by the addition of multifunctional carboxylic acids and acidanhydrides and in general by the curing methods described in U.S. Pat.No. 3,970,608, which is incorporated by reference. Radiationcrosslinking is preferred for adhesives because reactive ingredients donot come in contact with warm adhesives.

The materials of the present invention including in many casescrosslinked versions are useful in adhesives (including pressuresensitive adhesives, contact adhesives, laminating adhesives andassembly adhesives, labels, packaging adhesives, weatherable tapes),sealants, printing plates, oil gels, and maskants. Crosslinked forms ofthe invention are especially useful in applications requiring resistanceto elevated temperatures. However, it may be necessary for a formulatorto combine a variety of ingredients together with the polymers of thepresent invention in order to obtain products having the propercombination of properties (such as adhesion, cohesion, durability, lowcost, etc.) for particular applications. Thus, a suitable formulationmight contain only the polymers of the present invention and, e.g., acuring agent. However, in most adhesive and sealant applications,suitable formulations would also contain various combinations of resins,plasticizers, fillers, stabilizers and other ingredients such asasphalt. The following are some typical examples of formulations forsealants.

In adhesives and sealant applications, it is common practice to add anadhesion promoting or tackifying resin that is compatible with thepolymer, generally from 20 to 400 parts per hundred parts of polymer byweight. A common tackifying resin is a diene-olefin copolymer ofpiperylene and 2-methyl-2-butene having a softening point of about 95°C. This resin is available commercially under the tradename Wingtack® 95and is prepared by the cationic polymerization of 60% piperlene, 10%isoprene, 5% cyclo-pentadiene, 15% 2-methyl-2-butene and about 10%dimer, as taught in U.S. Pat. No. 3,577,398. Other tackifying resins maybe employed wherein the resinous copolymer comprises 20-80 weightpercent of piperylene and 80-20 weight percent of 2-methyl-2-butene. Theresins normally have ring and ball softening points as determined byASTM method E28 between about 80° C. and 115° C.

Aromatic resins may also be employed as tackifying agents, provided thatthey are compatible with the particular polymer used in the formulation.Normally, these resins should also have ring and ball softening pointsbetween about 80° C. and 115° C. although mixtures of aromatic resinshaving high and low softening points may also be used. Useful resinsinclude coumarone-indene resins, polystyrene resins, vinyl toluene-alphamethylstyrene copolymers and polyindene resins.

Other adhesion promoting resins which are also useful in thecompositions of this invention include hydrogenated rosins, esters ofrosins, polyterpenes, terpenephenol resins and polymerized mixedolefins, lower softening point resins and liquid resins. An example of aliquid resin is Adtac® LV resin from Hercules. To obtain goodthermooxidative and color stability, it is preferred that the tackifyingresin be a saturated resin, e.g., a hydrogenated dicyclopentadiene resinsuch as Escorez® 5000 series resin made by Exxon or a hydrogenatedpolystyrene or polyalphamethylstyrene resin such as Regalrez® resin madeby Hercules. Softening points of solid resins may be from about 40° C.to about 120° C. Liquid resins, i.e., softening points less than roomtemperature, may be used as well as combinations of solid and liquidresins. The amount of adhesion promoting resin employed varies from 0 to400 parts by weight per hundred parts rubber (phr), preferably between20 to 350 phr, most preferably 20 to 150 phr. The selection of theparticular tackifying agent is, in large part, dependent upon thespecific polymer employed in the respective adhesive composition.

A composition of the instant invention may contain plasticizers, such asrubber extending plasticizers, or compounding oils or organic orinorganic pigments and dyes. Rubber compounding oils are well-known inthe art and include both high saturates content oils and naphthenicoils. Preferred plasticizers are highly saturated oils, e.g. Tufflo®6056 and 6204 oil made by Arco and naphthenic process oils, e.g.Shellflex® 371 oil made by Shell. The amounts of rubber compounding oilemployed in the invention composition can vary from 0 to about 150 phr,preferably between about 0 to about 100 phr, and most preferably betweenabout 0 and about 60 phr.

Optional components of the present invention are stabilizers whichinhibit or retard heat degradation, oxidation, skin formation and colorformation. Stabilizers are typically added to the commercially availablecompounds in order to protect the polymers against heat degradation andoxidation during the preparation, use and high temperature storage ofthe composition.

Various types of fillers and pigments can be included in sealant andadhesive formulations. This is especially true for exterior sealants inwhich fillers are added not only to create the desired appeal but alsoto improve the performance of the sealant such as its weatherability. Awide variety of fillers can be used. Suitable fillers include calciumcarbonate, clays, talcs, silica, zinc oxide, titanium dioxide and thelike. The amount of filler usually is in the range of 0 to about 65% wbased on the solvent free portion of the formulation depending on thetype of filler used and the application for which the sealant isintended. An especially preferred filler is titanium dioxide.

If the adhesive or sealant will be applied from solvent solution, theorganic portion of the formulation will be dissolved in a solvent orblend of solvents. Aromatic hydrocarbon solvents such as toluene,xylene, or Shell Cyclo Sol 53 are suitable. Aliphatic hydrocarbonsolvents such as hexane, naphtha or mineral spirits may also be used. Ifdesired, a solvent blend consisting of a hydrocarbon solvent with apolar solvent can be used. Suitable polar solvents include esters suchas isopropyl acetate, ketones such as methyl isobutyl ketone, andalcohols such as isopropyl alcohol. The amount of polar solvent useddepends on the particular polar solvent chosen and on the structure ofthe particular polymer used in the formulation. Usually, the amount ofpolar solvent used is between 0 and 50% w in the solvent blend.

Combinations of primary and secondary antioxidants are preferred. Suchcombinations include sterically hindered phenolics with phosphites orthioethers, such as hydroxyphenylpropionates with aryl phosphates orthioethers, or amino phenols with aryl phosphates. Specific examples ofuseful antioxidant combinations include3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate)methane (Irganox® 1010 fromCiba-Geigy) with tris(nonylphenyl)phosphite (Polygard® HR fromUniroyal), Irganox® 1010 with bis(2,4-di-t-butyl)pentaerythritoldiphosphite (Ultranox® 626 from Borg-Warner).

Additional stabilizers known in the art may also be incorporated intothe composition. These may be for protection during the life of thearticle against, for example, oxygen, ozone and ultra-violet radiation.However, these additional stabilizers should be compatible with theessential stabilizers mentioned hereinabove and their intended functionas taught herein.

All adhesive and sealant compositions based on the polymers of thisinvention will contain some combination of the various formulatingingredients disclosed herein. No definite rules can be offered aboutwhich ingredients will be used. The skilled formulator will chooseparticular types of ingredients and adjust their concentrations to giveexactly the combination of properties needed in the composition for anyspecific adhesive, coating or sealant application.

Adhesives are frequently thin layers of sticky compositions which areused in protected environments (adhering two substrates together).Therefore, unhydrogenated epoxidized polymers will usually have adequatestability so resin type and concentration will be selected for maximumstickiness without great concern for stability, and pigments willusually not be used.

Sealants are gap fillers. Therefore, they are used in fairly thicklayers to fill the space between two substrates. Since the twosubstrates frequently move relative to each other, sealants are usuallylow modulus compositions capable of withstanding this movement. Sincesealants are frequently exposed to the weather, the hydrogenatedepoxidized polymers are usually used. Resins and plasticizers will beselected to maintain low modulus and minimize dirt pick-up. Fillers andpigment will be selected to give appropriate durability and color. Sincesealants are applied in fairly thick layers, solvent content is as lowas possible to minimize shrinkage.

A formulator skilled in the art will see tremendous versatility in thepolymers of this invention to prepare adhesives and sealants havingproperties suitable for many different applications.

The adhesive and sealant compositions of the present invention can beprepared by blending the components at an elevated temperature,preferably between about 50° C. and about 200° C., until a homogeneousblend is obtained, usually less than three (3) hours. Various methods ofblending are known to the art and any method that produces a homogenousblend is satisfactory. The resultant compositions may then be used in awide variety of applications. Alternatively, the ingredients may beblended into a solvent.

The adhesive compositions of the present invention may be utilized asmany different kinds of adhesives, for example, laminating adhesives,pressure sensitive adhesives, tie layers, hot melt adhesives, solventborne adhesives and waterborne adhesives in which the water has beenremoved before curing. The adhesive can consist of simply the polymeror, more commonly, a formulated composition containing a significantportion of the polymer along with other known adhesive compositioncomponents. A preferred method of application will be hot meltapplication at a temperature around or above 100° C. because hot meltapplication above 100° C. minimizes the presence of water and other lowmolecular weight inhibitors of cationic polymerization. The adhesive canbe heated before and after cure to further promote cure or post cure.Radiation cure of hot adhesive is believed to promote faster cure thanradiation cure at lower temperatures. The unhydrogenated precursors mayalso be used in these applications.

Preferred uses of the present compositions are the preparation ofpressure-sensitive adhesive tapes and the manufacture of labels. Thepressure-sensitive adhesive tape comprises a flexible backing sheet anda layer of the adhesive composition of the instant invention coated onone major surface of the backing sheet. The backing sheet may be aplastic film, paper or any other suitable material and the tape mayinclude various other layers or coatings, such as primers, releasecoatings and the like, which are used in the manufacture ofpressure-sensitive adhesive tapes. The unhydrogenated precursors mayalso be used in these applications.

Sealant compositions of this invention can be used for manyapplications. Particularly preferred is their use as gap fillers forconstructions which will be baked (for example, in a paint baking oven)after the sealant is applied. This would include their use in automobilemanufacture and in appliance manufacture. Another preferred applicationis their use in gasketing materials, for example, in lids for food andbeverage containers. The unhydrogenated precursors may also be used inthese applications.

EXAMPLES

Tables I through III demonstrate the advantages available fromdissimilar arm block copolymers in pressure sensitive adhesiveapplications.

Table IA illustrates two useful molecular structures which are withinthe invention, as well as a control polymer which is widely used in theadhesives industry. Molecular weights and other descriptive data aregiven in Table IB. The polymers within the invention contain side chainsof polyisoprene (2 and 4, respectively) and a saturated main chain ofpoly(ethylene/butylene) terminated with polystyrene blocks. The sidechains and main chain are joined at the mid-point of the main chainthrough a coupling agent. The control polymer is predominantly S--EB--Striblock (no side chains), with 30% or less of S--EB diblock.

The total molecular weights of the polymers of the invention bracketthat of the control polymer. Diblock content is lower than that of thecontrol. The coupling efficiency figures of 87 percent and 89 percent,respectively indicate diblock content is ≦13 percent and ≦11 percent,respectively. In spite of the similarity in molecular weight and lowerdiblock content, the solution viscosity of the dissimilar arm polymersis much lower than that of the control (Table IB). Compared toconventional 100 percent unsaturated block copolymers used in theadhesives industry, the viscosity reduction is also striking. Forexample, the viscosity of KRATON® D1107 Rubber, a conventional polymerthat has long been used in such applications, (20 percent in toluene) is514 cps, compared to 180 and 93 cps, respectively, for the inventionpolymers shown in Table IB. This viscosity reduction is valuable in bothpolymer manufacture and end use application; e.g., ability to use highersolids contents, less solvent, easier application, lower pumping energyrequirements, etc.

The polymers described in Table I were formulated in apressure-sensitive adhesive formulation to glass transition temperaturesof -20° C. (Table II) and -15° C. (Table III). Taken as a whole, theexperimental polymers were superior to the control polymer in tack, peelstrength and holding power to steel. Polymer #4918 was superior to thecontrol in SAFT to Mylar. The superiority in tack was evident inqualitative finger tack comparisons as well as laboratory instrumentaltack measurements.

In another example, Polymer #4918 was compared to the same controlpolymer using formulations calculated to give a Tg of -15° C. (TableIII). In this case, #4918 was superior to the control in tack, peelstrength and SAFT properties. It was somewhat inferior to the control inholding power to steel.

The ability to obtain a combination of high adhesive performance at lowmolecular weight and viscosity is attributed to the superior phaseseparation between polystyrene endblocks and poly(ethylene-butylene)rubber blocks compared to polystyrene and unsaturated diene rubberblocks.

                                      TABLE I                                     __________________________________________________________________________    Polymer Descriptions                                                          A. Polymer Structures - Examples                                               ##STR1##                                                                     B. Polymer Molecular           Conventional                                   Parameters             #4918                                                                             #4844                                                                             Polymer                                        __________________________________________________________________________    Styrene block mol. wt., M                                                                             9.3                                                                              6.0 5.3                                            Main chain rubber mol. wt., M                                                                        50  46  86                                             Double bonds in main chain hydrogenated, %                                                           >99 >99 >99                                            Side chain rubber mol. wt., M                                                                        18  3.8 No side chains.                                Number of side chains   2   4    0                                            Total mol. wt., M      94  73  86                                             Polymeric Styrene Content, %                                                                         17.9                                                                              16.7                                                                              13                                             Coupling Efficiency, % 87  89  71                                             Solution Viscosity, 20% wt. in toluene, cps                                                          180 93  1250                                           __________________________________________________________________________

                                      TABLE II                                    __________________________________________________________________________    Properties of Adhesive Formulations                                           (All formulated to Tg = -20° C.)                                       __________________________________________________________________________    A.                                                                              Formulations                                                                  Formulation Number  R-108 R-084 R-110                                         Base Polymer        #4918 #4844 Conventional                                                      (Invention)                                                                         (Invention)                                                                         Polymer                                       Base Polymer        100.0 100.0 100.0                                         Hydrocarbon Resin (softening pt., 85° C.).sup.1                                            102.4 103.7 108.2                                         Hydrocarbon Resin (softening pt., 18° C.).sup.2                                            144.5 146.4 152.8                                         Hindered Phenolic.sup.3 Antioxidant                                                               1.0   1.0   1.0                                           UV Stabilizer No. 1.sup.4                                                                         0.25  0.25  0.25                                          UV Stabilizer No. 2.sup.5                                                                         0.25  0.25  0.25                                          Total phr (parts per hundred rubber-the                                                           348.4 351.6 362.5                                         polymer)                                                                    B.                                                                              Properties                                                                    Rolling Ball Tack, cm                                                                             1.3   2.3   1.9                                           Polyken Probe Tack, kg                                                                            2.1   2.0   1.8                                           Loop Tack, oz/in    81    95    80                                            180 Deg. Peel Strength, pli                                                                       5.8   8.0   5.4                                           Holding Power/Steel, min                                                                          180   125   67                                            Holding Power/Kraft, min                                                                          1.4   3.5   3.5                                           SAFT, Mylar, deg. C.                                                                              64    48    50                                            SAFT, Kraft, deg. C.                                                                              <38   <38   <38                                           Thickness of Adhesive Film, mils                                                                  1.4   1.5   1.5                                         __________________________________________________________________________     .sup.1 Regalrez 1085; Hercules, Inc.; hydrogenated styrene/alpha methyl       styrene copolymers                                                            .sup.2 Regalrez 1018; Hercules, Inc.; hydrogenated styrene/alpha methyl       styrene copolymers                                                            .sup.3 Irganox 1010; CIBAGeigy Corp.                                          .sup.4 Tinuvin 327; CIBAGeigy Corp.                                           .sup.5 Tinuvin 770; CIBAGeigy Corp.                                      

                                      TABLE III                                   __________________________________________________________________________    Properties of Adhesive Formulations                                           Formulated to Tg = -15 deg. C.                                                __________________________________________________________________________    A. Formulations                                                                  Formulation Number  R-131  R-117                                              Base Polymer        #4918  Conventional                                                           (Invention)                                                                          Polymer                                            Base Polymer        100.0  100.0                                              Hydrocarbon Resin (softening pt., 85° C.).sup.1                                            132.9  138.0                                              Hydrocarbon Resin (softening pt., 18° C.).sup.2                                            100.5  95.2                                               Hindered Phenolic.sup.3 Antioxidant                                                               1.0    1.0                                                UV Stabilizer No. 1.sup.4                                                                         0.25   0.25                                               UV Stabilizer No. 2.sup.5                                                                         0.25   0.25                                               Total phr           334.9  334.7                                           B. Properties                                                                    Rolling Ball Tack, cm                                                                             2.6    7.2                                                Polyken Probe Tack, kg                                                                            2.3    0.83                                               Loop Tack, oz/in    101    95                                                 180 Deg. Peel Strength, pli                                                                       7.3    5.9                                                Holding Power/Steel, min                                                                          225    398                                                Holding Power/Kraft, min                                                                          6.3    6.7                                                SAFT/Mylar, deg. C. 70     62                                                 SAFT/Kraft, deg. C. 55     38                                                 Thickness of Adhesive Film, mils                                                                  1.5    1.4                                             __________________________________________________________________________     .sup.1 Regalrez 1085; Hercules, Inc.; hydrogenated styrene/alpha methyl       styrene copolymers                                                            .sup.2 Regalrez 1018; Hercules, Inc.; hydrogenated styrene/alpha methyl       styrene copolymers                                                            .sup.3 Irganox 1010; CIBAGeigy Corp.                                          .sup.4 Tinuvin 327; CIBAGeigy Corp.                                           .sup.5 Tinuvin 770; CIBAGeigy Corp.                                      

Though the polymers of this invention contain unsaturated arms ofhomopolymers, they behave primarily like the fully saturated blockcopolymers commonly used in adhesives when subjected to heat andaccelerated weathering. Table IV compares the viscosity and colorstability of a polymer of the invention with those of a conventionalsaturated polymer (see Table I) and a conventional unsaturated polymerwidely used in the industry (KRATON® D1107 Rubber, a linear S--I--S of160M molecular weight and 15 percent styrene content made by Shell OilCompany). Adhesive compositions based on these three polymers weresubjected to a temperature of 350° F. for 96 hours, with viscosity andcolor measured at various intervals. Such a test is important inpredicting the behavior of hot melt adhesive compositions. The polymerof the invention approximated the behavior of the fully saturatedpolymer in maintaining viscosity and color over time, and was markedlysuperior to the unsaturated polymer in these respects.

                  TABLE IV                                                        ______________________________________                                        Melt Stability                                                                              Conventional                                                                             Invention                                                                              Conventional                                Base Polymer  Saturated  Polymer  Unsaturated                                 of Formulation                                                                              Polymer.sup.(1)                                                                          #4918.sup.(1)                                                                          Polymer.sup.(2)                             ______________________________________                                        Time at 350 deg. F. hr.                                                                     Melt Viscosity, cps.sup.(3)                                      0            52,200     13,920   71,800                                       8            52,300     13,820   41,800                                      24            52,200     13,150   27,530                                      48            54,200     10,210   12,550                                      96            52,150     10,730   19,100                                                  Gardner Color                                                      0            1          1        10                                           8            3          3        13                                          24            4          4        14                                          48            6          10       17                                          96            6          11       15                                          ______________________________________                                         .sup.(1) Formulation: Polymer, 100 parts by weight (pbw); Regalrez 1085       resin, 125 pbw; Regalrez 1018 resin, 20 pbw; Irganox 1010, 1.0 pbw;           Tinuvin 770, 0.25 pbw; Tinuvin 327, 0.25 pbw.                                 .sup.(2) Formulation: Polymer, 100 pbw; Piccotac 95 resin, 135 pbw;           Shellflex 371 oil, 15 pbw; Irganox 1010, 1.0 pbw; Tinuvin 770, 0.25 pbw;      Tinuvin 327, 0.25 pbw.                                                        .sup.(3) Brookfield viscosity, Model RVTD.                               

For consideration as a polymer for weatherable adhesives, the inventionpolymers should withstand outdoor aging conditions as well as conditionsin laboratory devices designed to predict outdoor aging stability. TableV shows that an adhesive based on a polymer of the invention maintainspeel strength over time at least as well as a conventional saturatedpolymer-based adhesive. Furthermore, the mode of failure remains a cleanadhesive peel (which is desirable) whereas an adhesive based onunsaturated polymer begins to fail cohesively (that is, leaves a layerof adhesive on both the substrate and backing film) after a short agingperiod. This behavior of the unsaturated polymer-based adhesive isprobably due to weakening caused by degradation. Similar conclusions canbe drawn from results of accelerated aging studies, which are shown inTable VI.

                  TABLE V                                                         ______________________________________                                        Outdoor Aging                                                                 (45 deg. to south)                                                            Pressure Sensitive Tape                                                                   Conventional                                                                              Invention Conventional                                Base Polymer                                                                              Saturated   Polymer   Unsaturated                                 of Formulation                                                                            Polymer.sup.(1)                                                                           #4918.sup.(1)                                                                           Polymer.sup.(2)                             ______________________________________                                        Aging time, days                                                                          180 deg. Peel Strength, pli                                        0          4.1A.sup.(3)                                                                              6.4A      9.3A                                                  Aged through Glass                                                  15          6.0A        5.7A      9.5C                                        30          4.3A        5.1A      6.9C                                                  Aged through Mylar                                                  15          5.4A        6.3A      10.8C                                       30          4.6A        5.5A      7.5C                                        ______________________________________                                         .sup.(1) See footnote 1, Table IV.                                            .sup.(2) See footnote 2, Table IV.                                            .sup.(3) A signifies adhesive failure; C, cohesive failure.              

                  TABLE VI                                                        ______________________________________                                        Accelerated Aging                                                             (Laboratory QUV Cabinet, UVB 313 lamp)                                        Pressure Sensitive Tape                                                                  Conventional                                                                              Invention Conventional                                 Base Polymer                                                                             Saturated   Polymer   Unsaturated                                  of Formulation                                                                           Polymer.sup.(1)                                                                           #4918.sup.(1)                                                                           Polymer.sup.(2)                              ______________________________________                                        Aging time, hr.                                                                          180 deg. Peel Strength, pli                                         0         3.9A.sup.(3)                                                                              6.8A      8.8A                                                  Aged through Glass                                                   100        5.4A        5.1A      6.5C                                         300        2.7A        5.4A      4.9C                                         500        3.8A        3.1A      --.sup.(4)                                   ______________________________________                                         .sup.(1) See footnote 1, Table IV.                                            .sup.(2) See footnote 2, Table IV.                                            .sup.(3) A signifies adhesive failure; C, cohesive failure.                   .sup.(4) Backing failed.                                                 

Incorporating unsaturated polymer arms into a basically saturated blockcopolymer structure adds the potential for crosslinking of the system,with its attendant benefits in resistance to shear and heat in theapplication. The invention polymer is amenable to crosslinking using avariety of techniques. Table VII illustrates that electron beam (EB)radiation crosslinks an adhesive composition based on the inventionpolymer #4918 at doses of 10 and 16 megarads (gel contents of 38 percentand 81 percent of base polymer, respectively, are attained). Shearadhesion failure temperature (SAFT) is markedly improved without anymajor loss in tack properties.

The presence of unsaturated polymer arms in the otherwise saturatedinvention block copolymer increases the number of reaction sites forfunctionalization. The functionalized polymer frequently has improvedadhesion properties because of its increased polarity. Functionalizedpolymers also may be more reactive in radiation-induced crosslinkingprocesses. In the example of Table VII, electron beam radiation was usedto crosslink an adhesive formulation based on an invention polymer thathad been epoxidized. Crosslinking occurred at relatively low doses (aslittle as 2 or 6 megarads with gel contents of 14 percent and 74 percentof base polymer, respectively). Holding power and SAFT values wereincreased substantially with little or no effect on tack propertiesexcept at very high doses.

                                      TABLE VII                                   __________________________________________________________________________    Electron Beam (EB) Crosslinking.sup.(1)                                                                 Invention Polymer #4918,                                       Invention Polymer #4918                                                                      Epoxidized.sup.(2)                                  Dose, megarads                                                                           0  2  6  10 16 0  2  6  10  16                                     __________________________________________________________________________    Gel, % of base                                                                           0  0  0  38 81 0  14 74 97  88                                     polymer                                                                       Rolling Ball Tack, cm                                                                    1.8                                                                              1.7                                                                              1.8                                                                              2.3                                                                              2.3                                                                              3.1                                                                              2.3                                                                              2.6                                                                              4.7 6.8                                    Loop Tack, oz/in                                                                         51 38 54 48 48 57 75 61 58  51                                     Polyken Probe Tack,                                                                      .82                                                                              .89                                                                              .92                                                                              .90                                                                              .65                                                                              .64                                                                              .76                                                                              .73                                                                              .40 .52                                    kg                                                                            180 deg. Peel Str., pli                                                                  3.5                                                                              2.6                                                                              2.3                                                                              2.2                                                                              2.3                                                                              3.8                                                                              2.5                                                                              2.2                                                                              2.2 2.0                                    Holding Power to                                                                         197                                                                              489                                                                              574                                                                              152                                                                              183                                                                              14 75 778                                                                              >7000                                                                             --                                     Steel, min.sup.(3)                                                            SAFT.sup.(4) on Mylar,                                                                   82 87 91 114                                                                              127                                                                              82 83 113                                                                              118 114                                    deg. C.                                                                       __________________________________________________________________________     .sup.(1) Formulation: Polymer, 100 pbw; Regalrez 1085 resin, 54 pbw;          Regalrez 1018 resin, 68 pbw; Polygard HR antioxidant, 1.0 pbw. EB curing      was accomplished on an Energy Sciences, Inc., Electron Beam Unit, Model       CB150.                                                                        .sup.(2) Epoxidized to 1.26 meq/g by method described in U.S. Pat. No.        5,229,464.                                                                    .sup.(3) 0.5 in. × 0.5 in bond, 2 kg weight.                            .sup.(4) Shear Adhesion Failure Temperature of lap shear bond, 1 in           × 1 in, 2 kg weight.                                               

Similarly, epoxidized and non-epoxidized block copolymers of theinvention crosslink readily in adhesive formulations under ultravioletlight (UV). Table VIII illustrates results obtained using a LindePhotocure System from Union Carbide Corporation. Substantialcrosslinking took place on the epoxidized version even at the lowestdosages (highest belt speeds shown in Table VIII).

                  TABLE VIII                                                      ______________________________________                                        Crosslinking by Ultraviolet Light Radiation.sup.(1)                                           Invention                                                                              Invention                                            Base Polymer    Polymer  Polymer #4918                                        of Formulation  #4918.sup.(1)                                                                          Epoxidized.sup.(3)(4)                                ______________________________________                                                      Gel, % of base polymer                                          No dose         3.3      3.2                                                  Belt Speed, ft/min.sup.(5)                                                    56              13       89                                                   44              --       87                                                   32               9       90                                                   21               6       92                                                   7.5             41       90                                                   3.8             56       92                                                   ______________________________________                                         .sup.(1) Irradiated with UV light by the method described in U.S. Pat. No     5,229,464 which is herein incorporated by reference (Linde Photocure          Systems, Union Carbide Corp.).                                                .sup.(2) Formulation: Polymer, 100 pbw; Regalrez 1085 resin, 58 pbw;          Regalrez 1018 resin, 65 pbw; Polygard HR antioxidant, 1.0 pbw; Irgacure       651 photoinitiator, 1.0 pbw; 1,6 hexanediol diacrylate crosslinker, 7.5       pbw.                                                                          .sup.(3) Epoxidized to 1.26 meq/g by the method described in U.S. Pat. No     5,229,464.                                                                    .sup.(4) Formulation: Polymer, 100 pbw; Regalrez 1085 resin, 54 pbw;          Regalrez 1018 resin, 68 pbw; Polygard HR antioxidant, 1.0 pbw; Cyracure       UVI 6974 cationic photoinitiator, 1.1 pbw.                                    .sup.(5) The slower the belt speed, the higher the radiation dose.       

In Table IX, the results of a crosslinking study are presented in whichinitiation and propagation are chemical in nature, unaided by any formof radiation. The crosslinking agent is a urea-formaldehyde resin andthe reaction is catalyzed by dodecylbenzene sulfonic acid. Gel contentsof 80 to 90 percent are created over 20 to 40 minutes at 149° to 177° C.These results are illustrative of the fact that the unsaturated arms ofthe invention polymers will undergo a variety of chemical reactionsleading to network formation. Such structures improve servicetemperatures, solvent resistance and shear properties in adhesives,sealants, coatings, and many other applications.

                  TABLE IX                                                        ______________________________________                                        Chemical Crosslinking                                                         ______________________________________                                        Formulation                                                                   Invention polymer #4918                                                                      100.0      pbw                                                 Beetle ® 80.sup.(1)                                                                      11.1       pbw                                                 Cycat ® 600.sup.(2)                                                                      1.1        pbw                                                 Irganox 1010 antioxidant                                                                     0.5        pbw                                                 Polygard HR antioxidant                                                                      0.5        pbw                                                                113.2                                                          ______________________________________                                                       Cure Time, Gel (polymer basis)                                 Cure Temp., °C.                                                                       min.       Content, %                                          ______________________________________                                        149            20         80                                                  149            40         90                                                  177            20         87                                                  ______________________________________                                         .sup.(1) Urea-formaldehyde resin, American Cyanamid Co.                       .sup.(2) Catalyst, 70% solution of dodecylbenzene sulfonic acid in            isopropanol, American Cyanamid Co.                                       

We claim:
 1. Radial or star asymmetric block copolymers of the formula

    (A--HD).sub.x --Y--(UD).sub.z

wherein A is a vinyl aromatic hydrocarbon block having a peak molecularweight as determined by gel permeation chromatoqraphy of from 4000 to20,000, HD is a hydrogenated conjugated diene block having a peakmolecular weight as determined by gel permeation chromatography of from10,000 to 100,000, Y is a multifunctional coupling agent, UD is anunhydrogenated conjugated diene block having a peak molecular weight asdetermined by gel permeation chromatography of from 1000 to 80,000, theblock copolymer has a vinyl aromatic hydrocarbon content of from 4 to 35percent by weight, x is an integer from 2 to 20, z is an integer from 1to 10, and x+z ranges from 3 to
 30. 2. The copolymers of claim 1 whereinthe block copolymer is a radial block copolymer of formula (I) and x is2 to 4, z is 1 to 4 and x+z is 3 to
 6. 3. The copolymers of claim 1wherein the hydrogenated diene is butadiene and the unhydrogenated dieneis isoprene.
 4. Improved adhesive and sealant compositions comprisingthe copolymers of claim 1 and a tackifying resin.
 5. The compositions ofclaim 4 wherein the compositions are crosslinked.
 6. Improved adhesiveand sealant compositions comprising the copolymers of claim 2 and atackifying resin.
 7. The compositions of claim 6 wherein thecompositions are crosslinked.
 8. Improved adhesive and sealantcompositions comprising the copolymers of claim 3 and a tackifyingresin.
 9. The compositions of claim 8 wherein the compositions arecrosslinked.